1. Technical Field
The present disclosure relates to power devices and, more specifically, to power devices with high frequency capabilities.
2. Description of the Related Arts
For mobile applications, such as smart phones and tablets, RF power amplifiers (PA) are used. Besides high efficiency and high linearity, it is desirable to have a PA with low thermal resistance, excellent connection of source to ground and good shielding.
High frequency power amplifiers are dominated by devices based on wide band gap material substrates, such as GaAs. One advantage of a GaAs substrate as compared to silicon is higher carrier mobility and lower parasitic capacitance. One drawback for GaAs devices is that it is not compatible with main stream silicon process. So it is difficult to integrate a GaAs PA with other devices on the same die, which limits the performance of the system. In addition, the GaAs substrate is a semi-insulator, which has relatively poor thermal conductivity.
CMOS technology is well developed and in a very advanced mature stage for production. It is desired to develop RF PA based on CMOS technology. However, the low breakdown voltage of CMOS technology limits the power capability of CMOS and the high parasitic capacitance limits its high frequency capability. To make up the high voltage requirement for PA, a few NMOS devices are connected to each other. Unfortunately, this decreases the current capability and increases the parasitic capacitance resulting in an even worse performance. Moreover, the SOI layer isolates the heat transfer to the substrate, which degrades the PA's performance.